Centrifugal separation apparatus



C. L. AMERO CENTRIFUGAL SEPARATION APPARATUS 4 Sheets-Sheet 1 Filed Oct. 15, 1968 vm I. S H mm m om wm mm mm 8 Q Q Q Q 3 Oct. 6, 1970 Filed Oct. 15. 1968 C. L. AMERO 4 Sheets-Sheet 4 30I 3|3-" "BIZ I C 343 342 T I 370 D B A 3e4-\ v lL-AI (g) 356 360 Z) {5 II; II

338 334 339 33s 335 340 RAISE LOWER POOL POOL FIG 4 94 INCREASE CHEMICAL United States Patent Office 3,532,264 Patented Oct. 6, 1970 3,532,264 CENTRIFUGAL SEPARATION APPARATUS Clifford Leonard Amero, East Walpole, Mass., assignor to Bird Machine Company, South Walpole, Mass, a

corporation of Massachusetts Filed Oct. 15, 1568, Ser. No. 767,724 Int. Cl. B04b 11/02 US. Cl. 2337 15 Claims ABSTRACT OF THE DISCLOSURE Centrifuges of the continuous type, having a solid bowl portion to which the slurry is fed to form a pool, are provided with means for automatically adjusting the pool depth under the control of signals from a consistency analyzer for one of the fractions separated by the centrifuge, or under the interrelated control of signals from consistency analyzers for two or more such fractions, which signals may also be applied to control the rate of addition of a chemical to the slurry.

This invention relates to centrifugal separation apparatus for separating solids from a liquid slurry thereof. More particularly the invention concerns such apparatus which includes one or more centrifuges of the type which have an imperforate rotary bowl portion to which the slurry is fed to form a pool, a conveyor rotatable within and relative to this bowl portion to discharge continuously therefrom a slurry fraction containing solids which segregate toward the bowl under the centrifugal force, and an outlet for continuously removing another slurry fraction containing solids which do not sufliciently so segregate.

The object of the invention is to provide such centrifuges with control equipment for automatically regulating the operation thereof to maintain the same at or close to maximum effectiveness and efficiency of solids separation, despite fluctuations in feed rate, concentration and/or composition and with a minimum of chemical addition, if chemical is needed to assist the separation.

The invention features mechanism for regulating the depth of the slurry pool within the centrifuge bowl which is automatically actuated under the control of consistency analyzing equipment for one or more of the fractions separated by the centrifuge. It has been discovered that for many centrifuge applications pool depth regulation is extremely important and may even be critical to satisfactory operation of the centrifuge, affecting the solids content of all solids fractions separated which are normally two in number, that which contains the solids separating toward the bowl, termed herein the solids fraction, and the remaining fraction termed herein the effluent fraction, although three or more fractions may be separately collected. The usual effect of increasing pool depth is to increase the amount of the finer, lighter solids which are removed in the solids fraction. This in turn normally decreases the consistency of the solids fraction or, in other words, provides a wetter cake. Decreasing the pool depth ordinarily has the opposite effects. Pool depth regulation is therefore an effective tool with which the solids consistency of these fractions can be controlled.

Centrifuges equipped for manual pool depth adjustment while the centrifuge is running are commercially available, one such being disclosed in Cook U.S. Pat. No. 3,279,688, issued Oct. 18, 1966, wherein a skimmer which removes the eflluent fraction is manually adjustable to vary the pool depth. These are usually adjusted at start up to provide a pool depth satisfactory with the feed then coming to the machine and simply left in that condition until some fluctuation in feed rate, consistency or composition, or some other variable, causes the centrifuge to operate unacceptably at this setting. By the time a new and satisfactory adjustment can be made unpleasant consequences may have occurred in subsequent operations dependent on consistency within certain limits of an output fraction of the centrifuge. Even the few plants that maintain substantially constant manual supervision over centrifuge operation, with periodic consistency analyses as guides, have great difiiculty in maintaining a pool adjustment which is satisfactory as feed conditions fluctuate.

Where it is important to maintain the consistency of the solids fraction within a predetermined range, as it usually is, I prefer to control the automatic operation of the pool level adjustment mechanism at least primarily by signals from a consistency analyzer which is capable of determining and signaling the consistency of the solids fraction, or a representative portion thereof, preferably on a continuous basis. If consistency of the solids fraction is the only consideration, such automatic system will adjust the pool depth at start up to a setting which then produces a solids fraction within the desired consistency range, and automatically changes the depth to maintain that consistency despite fluctuation of the variables. However, the solids consistency of the other fraction or fractions is usually important too and is also affected by changes in the pool depth. Hence preferred apparatus according to the invention also includes an analyzer for another fraction, the effluent fraction being the only other fraction usually involved, this analyzer being also capable of determining and signaling consistency of the fraction or a representative sample thereof. These latter signals may be used to modify pool level adjustment in a direction which will provide a more desirable consistency in the other fraction so long as the solids fraction consistency remains within the desired limits. This arrangement, in which the solids fraction analyzer has primary control to maintain that fraction at desired consistency, is preferred except in cases in which consistency of that fraction is relatively unimportant. In such cases, the other analyzer may exert a more primary role.

in many cases addition of chemical to the slurry is required, either periodically or regularly, to assist the centrifuge in making the required separation. Such chemical, usually one or more of the many flocculants which are commercially available, functions to cause fioc formation in the fine, light particles, which fioc is more readily separated into the solids fraction by the centrifugal force. This not only reduces the solids consistency of the other fraction 'but it also often produces a lower consist ency, wetter solids fraction. In cases Where chemical is used, the invention preferably provides means for automatic regulation of the chemical feed rate under the control of both analyzers, with substantial benefits in maintaining feed of expensive chemical at a minimum consistent with all requirements of centrifuge performance.

The invention will now be more particularly described with reference to the accompanying drawings of preferred embodiments, wherein:

FIG. 1 is a view partly in vertical section partly in side elevation with parts broken away of a centrifuge of the type concerned equipped with pool level adjustment mechanism according to FIGS. l-3b of said Cook Pat. 3,279,685, with certain modifications and additions for purposes of enabling controlled operation of said adjustment means and chemical addition in accordance with the present invention;

FIG. 2 is a system diagram of a centrifuge such as that 3 of FIG. 1 connected to control equipment according to the present invention;

FIG. 3 is a circuit digaram showing electric circuitry suitable for operating the apparatus of FIG. 2;

FIG. 4 is a modification of the circuit diagram of FIG. 3.

Referring to FIG. 1, the centrifuge casing has at one end a solids receiving and discharging compartment 12. The centrifuge, of the solid bowl continuous type, has a bowl 14 which is cylindrical in part and frusto-conical toward the solids discharge end. One end plate of the bowl is fastened to a hollow drive shaft 16 which is rotated by suitable drive mechanism (not shown). The other end of the bowl is connected by a spider 18 to a hollow shaft 20 which is rotatably received in bearing 22 mounted on suitable support structure 24. The conveyor has a hollow hub 26 to one closed end of which is connected a drive shaft 28 rotatably mounted within shaft 16 and rotated at a slight differential to the bowl speed in the same direction as the bowl through differential gearing (not shown) connected to shaft 16. The other end of hub 26 has a flange 30 provided with a sleeve which is rotatable on a bushing 32 in which is rotatably journaled a sleeve 34 on bowl shaft 20. One or more conveyor blades 36 are secured to hub 26 and extend spirally around the hub substantially from end to end thereof and having the outer edge thereof close to the inner surface of the bowl.

Conveyor hub 26 is provided adjacent the frustoconical section of the bowl with a generally cylindrical chamber member 38 extending outwardly to the vicinity of the inner surface of the bowl and provided with inlet openings 40. A skimmer 42 with an inlet 44 has an annular flange 46 mounted on eccentric flanges 48 on a sleeve 50 which extends coaxially through bowl shaft 20 and is fixedly connected to a cantilever support ring 52 on support structure 24. Skimmer 42 removes the effluent fraction from the pool and discharges it through ports 54 into sleeve 50 from which it discharges through effluent pipe 56. The skimmer 42 is rotated on eccentric flanges 48 to adjust its distance from the bowl and consequently the pool depth by means of a block 58 on rotary feed pipe section 60 extending through sleeve 50 to a rotatable support 62, and by a gib and slide connection designated generally 64 which is fully shown and described in the aforesaid Pat. No. 3,279,688. Feed pipe section 60 has its outlet located in an end compartment 66 of conveyor hub 26. -It is rotated to adjust the skimmer and pool level by means of a worm gear 68 fixedly mounted on rotatable support 62 and worm shaft 70 rotatably mounted in a gear housing 72.

The structure so far described is disclosed in Pat. No. 3,279,688 aforesaid to which reference may be had for a more detailed explanation. Modifications for purposes of the present invention include a collecting hopper 74 mounted on a wall of solids discharge compartment or chute 12 in position to continually catch a representative portion of the discharging solids for analysis. Hopper 74 discharges via outlet opening 76 to a pipe partially shown at 78 through which it is pumped through analyzing equipment as will be hereinafter described, and returned to chute 12 by a pipe partially shown at 80. An outlet branch pipe partially shown at 82 is provided in effluent discharge pipe 56 through which a representative portion of the effluent is pumped to analyzing equipment as hereinafter described and returned to pipe 56 via a return pipe partially shown at 84.

Slurry feed pipe section 60 extends beyond rotatable support 62 and is rotatably coupled to one end of a fixed T-pipe 86 connected to a source of feed slurry (not shown). A smaller feed pipe 88 for flocculant or other chemical extends through the other closed end of T-pipe 86 and is rotatably coupled to a section 88 which extends coaxially through pipe 60 to an outlet in the wall of pipe 60 into a chamber 90 in conveyor hub 26 immediately adjacent slurry feed chamber 66 and provided with nozzles 92 for discharging the chemical to the slurry pool in the bowl. The hand wheel shown in Pat. 3,279,688 for operating worm shaft 70' has been replaced with a reversible electric motor with reduction gearing, indicated generally by the numeral 94.

Reference will now be made to FIG. 2 which is a system diagram in the nature of a flow sheet wherein control equipment is utilized in combination with the centrifuge of FIG. 1 in accordance with the invention. In this diagram, materials flow is indicated by lines with solid head arrows while control signal transmission is indicated by lines with open head arrows. The same reference numerals as in FIG. 1 are applied to diagrammatic representations of the same mechanism.

Pipe 78, which in FIG. 1 is connected to the outlet from solids discharge sample collection hopper 74, leads to a continuously running pump which discharges through line 102 to a consistency analyzer indicated gen erally by the reference numeral 104. While other types may be used, analyzer 104 is indicated as a measuring device produced commercially under the registered trademark Dynatrol by Automation Products, Inc. of Houston, Tex., which has been found to be a. particularly satisfactory and reliable device for the purpose, not being sensitive to changes in ambient temperature, viscosity, pressure orflow velocity.

In this type of analyzer, a portion of the solids discharge fraction is pumped via pipe 102 through a U-tube 106 which is mounted at its ends in the end wall of a cell 108 in which the tube is free to vibrate. Such vibration is produced by means of an arm 110 having a cross bar in a transverse housing 112 which at one end has an armature that is vibrated to vibrate the tube by a drive coil excited by a pulsating current. The other end of the cross bar also carries an armature the movement of which is sensed by a pick-up coil in the other end of housing 112 which provides an electric output signal that is a function of the density of the sample being analyzed in tube 106 and which can be translated into consistency according to the specific gravity of the solids being separated. This AC output signal is fed via line 114 to a converter 116 where it is converted to a 0-10 mv. DC signal which is supplied over line 118 to the control circuitry designated by blocks labeled CC and which will be described in connection with FIGS. 3 and 4.

The signal from analyzer 104 may be utilized by the control circuitry to cause pool depth adjustment operation of motor 94 in either direction (raise or lower) as indicated by full line 120 and/or to cause change in operation of the chemical feed pump as hereinafter described as indicated by dotted line 122. The solids fraction analyzed continuously exits from tube 106 and returns via pipe 80 to the solids discharge chute 12 from which the solids fraction is pumped or conveyed to further processing or disposal, as indicated by line 124.

A representative sample of the eflluent fraction leaving the centrifuge through pipe 56 flows through pipe 82 to a consistency analyzer designated generally 130. While other types may be used, analyzer is diagrammatically indicated as a turbidity measuring device produced commercially by the Bailey Meter Company of Wickliffe, Ohio. In this device, the sample flows between a light source 132 and a detector cell 134 exposed to the light source through the sample. The amount of radiant energy detected by cell 134 has a relationship to the concentration of suspended solids which is translated by electric circuitry into an output signal on line 136 indicative of the solids concentration. This signal is fed via receiverrecorder 138 and line 140 to the control circuitry, which may apply it as a speed variation signal over line 142 to a variable speed drive 144 on a pump 146 connected by pipe 148 to a suitable source of chemical (not indicated) and by pipe 150 to pipe 88 through which the chemical is supplied to the slurry pool in the centrifuge. The signal on line 140 may be utilized in addition or in the alternative to operate the pool depth adjustment motor 94 as indicated by the dotted line 152. A pipe 154 connects a suitable source of slurry .(not indicated) with T-pipe 86 and centrifuge feed pipe section 60.

After passing through the consistency analyzer 130, the sample of effiuent fraction is returned via pipe 84 to pipe 56 which carries the effluent fraction to further processing or discharge, as indicated by line 156. The variable speed drive 144 may suitably be a Reeves Model 051- M-18, /2 HP with reversible adjustment motor and reduction gear unit 158 like the motor and gear unit 94 connected to the pool depth adjustment shaft.

The specific consistency analyzers discussed above are capable of reliably determining consistency at the greatest dilution likely to be encountered in the respective fractions. In case either fraction has a solids consistency above the maximum of the satisfactory operating range of its analyzer, either the sample going to the analyzer can be diluted with clear water, the instrumentation being adjusted to correlate the measurement of the diluted sample with the consistency of the undiluted fraction, or other types or makes of analyzer more suitable for high consistency determinations may be substituted.

In some cases, more than two fractions may be separated by the centrifuge. For example, a third fraction may be segregated between a fraction closest to the bowl and a fraction closest to the axis. Such third fraction may be separately removed by providing the centrifuge of FIG. 1 with a second adjustable skimmer which has its inlet disposed radially outwardly of the skimmer removing the innermost fraction, or by providing the skimmer with two inlets and outlets, one inlet disposed radially outwardly of the other. In the case of such additional fractions separations, additional consistency analyzing equipment such as that described above may be provided for determining the consistency of the additional fractions and to provide signals utilized by the control circuitry in the control of p001 depth.

Reference will now be had to FIG. 3 which is a circuit diagram of control circuitry that may be employed in the arrangement of FIG. 2 in cases in which regulation of the consistency of the solids fraction is the primary concern. In this diagram, components shown in FIG. 2 bear the same reference numerals. In FIG. 3, a capital letter in a circle designates a relay and the same capital letter not in a circle designates a switch operated by that relay. A normally open switch controlled by a relay is designated by a gap in the circuit line between two spaced lines plus the corresponding letter while a normally closed switch controlled by a relay is designated by two lines across the circuit line and a slash line through them, plus the corresponding letter.

Lines 300, 301 are connected to a suitable source of electric current for operating the controls, which may be 115 volt-60 cycle AC line .300 having a manually operable control switch 302. Lines 304, 305 connects lines 300, 301 to the converter 116 of the solids fraction analyzer 104, the output signal of which is supplied by lines 306- 309 (designated generally 114 in FIG. 2) to converter 116. A time pulsing unit 310 is connected by lines 312, 313 to lines 300, 301. Unit 310 is designed to produce at desired intervals an output pulse of desired duration, and may for example be the Eagle Signal Co. Flexopulse Bulletin 320HG-92A6.

The pulse from unit 310 is supplied by circuit lines 314, 315 to an amplifier and controller system 316 which is supplied with the 0l0 mv. DC signal from converter 116 via lines 318, 319 (designated generally 118 in FIG. 2). System 316 is designed to convert this signal into amplified outputs on two different circuits respectively if the signal indicates the solids fraction consistency is higher or lower than the predetermined desired value or range, and otherwise to have no output. It may for example be a Rustrak Model 157-D DC Amplifier Recorder System 60 cycle AC.

System 316 produces an output in circuit 320, 321 when the signal from converter 116 indicates that the consistency of the solids fraction is too low. On receiving this output, starter 324 operates motor 94 in the direction to move the centrifuge skimmer radially outwardly toward the bowl thereby decreasing the pool depth, as indicated by lines 334336 and the legend Lower Pool. Conversely, system 316 produces an output in circuit 322, 323 when the signal from converter 116 indicates that the consistency of the solids fraction is too high. On receiving this output, starter 324 operates motor 94 in the direction to move the centrifuge skimmer radially inwardly away from the bowl, thereby increasing the pool depth as indicated by lines 338-340 and the legend Raise Pool.

The control system so far described is adequate for automatically regulating the pool depth in accordance with consistency changes in the solids fraction to maintain a desired consistency. This may be the only automatic control needed, as in cases where the turbidity of the effiuent fraction is of minor consequence and chemical dosage is not utilized or is independently controlled. The remainder of the FIG. 3 diagram shows additional circuitry which may advantageously be utilized for automatic chemical dosage control and for exerting additional pool depth control under the supervision of the pool depth control circuitry just described.

A circuit having lines 342, 343 is connected by lines 344, 345 and 346, 347 for opposite operation of the reversible speed control 158 of motor 144 on chemical pump 146. Line 346 has a normally open svvitch C and line 344 a normally open switch D. When switch D is closed the reversible speed control 158 is connected to circuit 342, 343 to reduce the speed of pump 146 and hence reduce the rate of chemical feed, as indicated by the legend Decrease Chemical. When switch C is closed the reversible speed control 158 is connected to circuit 342, 343 to increase the speed of pump 146 and hence to increase the rate of chemical addition, as indicated by the legend Increase Chemical. Circuit line 342 includes two normally closed switches A and B which are opened respectively by relay A in circuit 320, 321 when that circuit has an output from system 316 and by relay B in circuit 322, 323 when that circuit has an output from system 316. Thus switch A or switch B is opened whenever system 316 receives a signal calling for pool depth adjustment.

Circuit lines 300, 301 are connected to a voltage regulator and step down transformer 350 which is operatively connected to the solids consistency analyzer for the efliuent fraction by circuit lines 352, 353 and to receiver recorder 138 by circuit lines 354, 355. Signals from analyzer 130 to receiver recorder 138 via lines 356358 (designated generally 136 in FIG. 2) close switch 360 to relay C when the signals are indicative of consistency too high and close switch 362 to relay D when the signals are indicative that the consistency is below the desired value or range. When switch 360 is closed, relay C closes normally open switch C in line 346 connecting reversible speed control 158 to increase the rate of chemical dosage provided the consistency of the solids fraction is satisfactory so that both normally closed switches A and B in line 342 are closed. Also a circuit 364, 365 connecting circuit 342, 343 to the pool depth increase side of the reversing starter for motor 94 has a normally open switch C in line 364 which is closed by relay C, so that whenever chemical feed rate is increased the pool depth adjustment mechanism is operated to increase the pool depth. A normally open switch B in line 323 controlled by relay B in circuit 322, 323 isolates system 316 from circuit 364, 365 when that circuit is operative.

When switch 362 is closed, relay D closes normally open switch D in line 344 connecting reversible speed control 158 to decrease the rate of chemical dosage provided the consistency of the solids fraction is satisfactory.

If desired, additional circuitry with manually operated switches may be provided for operating reversing starter 324 and speed change control 94 when automatic supervision is not desired.

In cases where control of solids consistency in the effiuent fraction is of more importance than control of consistency of the solids fraction it may be desirable to revise the control circuitry of FIG. 3 to give the efiluent fraction consistency analyzer primary control over the solids fraction consistency analyzer. FIG. 4 shows such a revision, only so much of the circuitry of FIG. 3 being repeated as is required to show the changes.

Referring to FIG. 4 it will be seen that a normally open switch C has been included in line 315 of circuit 314, 315, between system 316 and circuit 342, 343. By virtue of this change, system 316 is operative to exert control over pool depth change only while the consistency of the effluent fraction is too high and therefore relay C closes the said switch C. Normally closed switches A and B have been moved from circuit 342, 343 to line 365 of circuit 364, 365. An additional relay E has been included in circuit 364, 365, relay E controlling a normally closed switch E which has been added to line 346 of circuit 346, 347 and a second normally closed switch B has been added in line 365 between relay E and line 323. A new circuit 370, 371 has been added between the pool depth lowering circuit 320, 321 and circuit 342, 343, this additional circuit including a normally open switch D controlled by relay D of the effluent fraction sensing control. A normally open switch A is included in line 321, controlled by relay A in circuit 320, 321.

With the changes just described, when the solids concentration of the effiuent fraction is too high as sensed by analyzer 130, and so long as it remains too high, the three normally open switches C are closed by relay C. If the signals from the solids fraction analyzer via circuit 318, 319 indicate a solids consistency too low, system 316 provides an output in circuit 320, 321. Normally open switch A is closed by relay A so that the output in circuit 320, 321 is effective to lower the pool by way of reversing starter 324. Normally closed switch A is opened by relay A so that circuit 364, 365 is deactivated despite the closing of its switchv C by relay C. Normally closed switch E therefore remains closed and the chemical feed rate changer 158 is operated to increase the rate of feed, via circuit 346, 347, closed switches C and E, circuit 342, 343 and pulsing unit 310. Similarly, when the consistency of the solids fraction is too high, circuit 322, 323 is effective to cause increase of pool depth by the closing of switch B by relay B while circuit 364, 365 is deactivated by the opening of normally closed switches B by relay B. By virtue of the opening of both normally closed switches B, relay E is not activated, and the circuit through lines 346 and 347 remains operative to simultaneously increase chemical feed rate.

When the consistency of the solids fraction is satisfactory so that system 316 has no output, it is desirable to raise the pool without increasing the chemical feed rate until the solids fraction consistency becomes too low or the efiluent fraction consistency becomes satisfactory. This is accomplished via circuit 364, 365, all four switches of which are now closed, activating relay E to open switch E, deactivating the increase chemical circuit.

When the solids consistency of the effluent fraction drops below the desired operating maximum, relay C is deactivated by the opening of switch 360 causing switches C to open. This deactivates the system 316 so that no control is exercised by the solids fraction analyzer, and tdeactivates circuits 346, 347 and 364, 365. Switch 362 8 closes activating relay D which closes switch D in circuit 344, 345 to circuit 342, 343 to operate speed changer 158 in the direction to decrease the rate of chemical feed, and closes switch D in circuit 370, 371 to circuit 342, 343 to operate reversing starter 94- in the direction to lower the pool depth. Such operation continues until the effluent fraction consistency again becomes too high.

It will be appreciated that in the system illustrated in FIG. 4, the consistency control equipment for the solids fraction is used primarily to provide a pool depth con sistent with maintaining the desired consistency of the efiluent fraction with a minimum use of chemical. While it is not recommended, it is possible to operate the pool depth and chemical feed rate change equipment solely from the efiluent fraction analyzer and controls. For example, with system 316 and connections to and from it eliminated, together with relays A, B and E and the switches they control, the system of FIG. 4 would be operative to cause increase of the pool depth and of chemical feed rate whenever the efiluent fraction consistency is too high and to lower the pool and decrease the chemical feed rate whenever the effluent fraction con sistency is below a predetermined level. Suitable mechanical stops would prevent pool depth adjustment beyond desirable limits. Other changes in the control circuits of FIGS. 3 and 4 can of course be made, these being merely illustrative of preferred arrangements.

The use of pulses from a timer to operate the controls is not essential but is desirable, since the spacing between operating pulses gives each adjustment an opportunity to produce a consistency change which is detected by the analyzing equipment before the next succeeding pulse. Thus, over-adjustment is minimized. In addition, the utilization of pulses increases the time in which an adjustable mechanism can be adjusted over its entire range, so that less reduction gearing from motors is required.

In some cases, chemical addition will be needed only intermittently when fluctuations from normal of feed rate, consistency or composition occur. In such cases, a startstop switch can be provided for chemical pump motor 144 which is actuated to stop from the speed reducer 158 when a predetermined minimum speed is reached and is actuated to start by a circuit controlled by relay C.

I claim: 1. In centrifugal separation apparatus which includes a centrifuge of the type having a rotatable solid bowl portion, means for continuously feeding a solids-liquid slurry into said bowl portion, conveyor means rotatable within and relative to said bowl portion for continuously discharging therefrom a first fraction of said slurry containing solids which segregate toward the bowl, and effluent outlet means for continuously discharging from said bowl portion a second fraction containing other solids, the combination of:

pool adjustment means for variably regulating the depth of said pool while the centrifuge is operating;

sensing means for making determinations of the solids consistency of at least one of said fractions and providing indications of such determinations;

and pool depth control means for connection between said sensing means and said pool adjustment means and responsive to said indications from said sensing means to cause regulation of the depth of said pool by said adjustment means in accordance with the nature of said indications.

2. The combination of claim 1 wherein said pool depth control means is responsive to indications from said sensing means to cause increase of said pool depth by said adjustment means when said indications are indicative of solids consistency above a predetermined value.

3. The combination of claim 1 wherein said pool depth control means is responsive to indications from said sensing means to cause decrease of said pool depth by said adjustment means when said indications are indicative of solids consistency below a predetermined value.

4. The combination of claim 1 wherein said sensing means includes two sensing devices for making said consistency determinations of said two fractions respectively and providing said indications thereof.

5. The combination of claim 1 which includes chemical feed means for feeding to the slurry chemical for promoting segregation of solids toward the bowl, regulating means for said chemical feed means for variably regulating the amount of said chemical fed thereby to the slurry, and chemical feed control means for connection between said sensing means and said regulating means and responsive to said indications from said sensing means to control the regulation of feed of said chemical by said regulating means in accordance with the nature of said indications.

6. The combination of claim 5 wherein said sensing means is a sensing device for making said determinations of the consistency of said first fraction only.

7. The combination of claim 5 wherein said sensing means is a sensing device for making said determinations of the consistency of said second fraction only.

8. The combination of claim 5 wherein said sensing means includes a first sensing device for making said determinations of the consistency of said first fraction and a second sensing device for making said determinations of the consistency of said second fraction.

9. The combination of claim 8 wherein said pool depth control means and said chemical feed control means are responsive to consistency indications from both of said sensing devices.

10. The combination of claim 9 wherein said pool depth control means is rendered responsive to indications from said first sensing device to cause regulation of the pool depth in accordance therewith by predetermined indications from said second sensing device.

11. The combination of claim 10 wherein said predetermined indications from said second sensing device also render said chemical feed control means responsive to predetermined indications from said first sensing device to cause increase in the chemical feed rate.

12. The combination of claim 11 wherein other predetermined indications from said second sensing device render said chemical feed control means responsive to said other predetermined indications to cause reduction of the chemical feed rate.

13. The combination of claim 12 wherein said other predetermined indications render said pool depth control means responsive to said other predetermined indications to cause decrease of the pool depth.

14. The combination of claim 8 wherein said pool depth control means is responsive to indications from said first sensing device to cause regulation of the pool depth in accordance therewith and said chemical feed control means is rendered responsive to indications from said second sensing device to cause regulation of the chemical feed rate in accordance therewith by predetermined indications from said first sensing device.

15. The combination of claim 14 wherein said pool depth control means is also responsive to predetermined indications from said second sensing device to cause increase of said pool depth.

References Cited UNITED STATES PATENTS 2,532,792 12/1950 Svensjo 233l9 3,279,687 10/1966 Amero 233--7 3,279,688 10/1966 Cook 2337 3,423,015 1/1969 OConor 233--7 ROBERT W. JENKINS, Primary Examiner US. Cl. X.R. 233-19 UNITED I STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 532 ,264 October 6 1970 Clifford Leonard Amero It is certified that error appears in the above identified patent and that said Letters Patent are hereb corrected as shown below:

Column 8, line 48, after "portion" insert to form a pool Signed and sealed this 6th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Attesting Officer 

